1. Field of the Invention
The present invention relates to a fuser roll used, for example, as a fuser roll for reprography machines.
2. Description of the Prior Art
Hitherto, as a fusing system of dry copying machines, so-called hot press fusing by using a heated roll is most generally employed. Generally the surface layer of the fuser roll used in this hot press fusing is made of a fluororesin or a silicone rubber and in many cases the oil fuse method is used wherein a silicone oil is supplied onto the surface of the roll at all times so as to prevent an offset phenomenon that causes part of toner to be transferred to the surface of the roll. Since, out of such rolls, the silicone rubber fuser roll is conventionally made of a dimethylpolysiloxane or a methylvinylpolysiloxane as a major raw material, there are such problems that when a silicone oil is supplied onto the roll surface at all times, the silicone rubber forming the roll surface layer is swelled with the silicone oil to cause the strength to be lowered and to cause the size of the roll to be changed, which does not allow the nip width to be kept stably.
In order to improve the durability of fuser rolls, a roll of which silicone rubber surface layer is coated, for example, with a PTFE (polytetrafluoroethylene), an FEP (tetrafluoroethylene/hexafuloropropylene copolymer), an ETFE (tetrafluoroethylene/ethylene copolymer), a PFA (tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer) is also developed (Japanese Patent Publication) (kokoku) No. 47-20747, but the surface is composed of a hard resin and therefore there is a defect that the copied image does not become sharp.
As a method of increasing the resistance of silicone rubbers to silicone oils, it is known to introduce as organic groups of the organopolysiloxane that is conventionally a major raw material of silicone rubbers, fluorine-containing groups, such as 3,3,3-trifluoropropyl groups. According to this method, it can be suppressed that the fluorosilicone rubber is swelled with a silicone oil and that the strength is lowered. However, since fluorosilicone rubbers are high in friction coefficient, the friction of the roll surface during the fusing run is high and therefore the roll surface is apt to be abraded and roughened. As a result, such problems arise that good copying becomes impossible and that offset is liable to occur because the releasability of the fuser roll from paper is poor.